1. Technical Field
The present invention generally relates to methods and apparatus for selecting a radio access technology at a multi-mode wireless communications device. In particular, the present invention relates to methods and apparatus for selecting a radio access technology that minimizes the energy consumption required to support a desired operating mode at the wireless device.
2. Background
For the foreseeable future, a variety of wireless communications systems will exist in parallel. For example, several cellular systems co-exist today in many regions. A single wireless operator may maintain a GSM network as well as a Wideband Code-Division Multiple Access (W-CDMA) network, with overlapping coverage between the two. Multiple operators may also maintain different radio access technologies in any given area, with varying degrees of interoperability permitted between them. As wireless systems continue to evolve, additional standards-based cellular technologies, such as those developed by the 3rd Generation Partnership Project (3GPP) as part of its “Long-Term Evolution” (LTE) initiative, will also be deployed, often in parallel with previously available technologies. In addition to the cellular systems, other wireless technologies, such as wireless local area network (WLAN) and “WiMax” technologies, will be widely available, often side-by-side with each other and with cellular technologies.
Furthermore, deployment of a given technology at any given time is likely to be uneven, with operators providing different stages of technology evolution at different locations. For example, with respect to 3GPP's W-CDMA technology, even a single operator might have different releases, such as Release 5, 6, or 7 of 3GPP's High-Speed Packet Access (HSPA) technology, deployed at different locations.
Thus, at any given time, a wide variety of radio access technologies (RATs) will be accessible to a mobile wireless device as it moves from region. Frequently, multiple RATs will be accessible at the same location, offering similar or overlapping services, such as voice, data, or messaging services.
Multi-mode wireless devices, i.e., devices designed to support two or more RATs, are now commonly available. These devices are also evolving to support more radio access technologies and to provide enhanced services and more flexibility to their users.
In the typical multi-mode device, selection between multiple radio access technologies is governed by pre-determined preferences established by a wireless operator. These preferences are typically enforced by means of codes programmed into a Subscriber Identity Module (SIM) card provided by the operator, which regulate a user's access to services. Thus, a wireless device will typically attempt to connect to a “preferred” RAT, provided that it is available at the device's current location. If it is not available, then a next-preferred RAT will be accessed.
In today's devices, the preferred RAT is not chosen with optimal power consumption at the wireless device in mind. In fact, the selection of the RAT can have serious implications for the energy consumption at the wireless device, and thus for the battery life between re-charging. These implications vary, depending on which services are used by the wireless device. Thus, depending on the operating mode of the wireless device, energy consumption will vary. In addition, for any given operating mode, energy consumption at the wireless device will vary depending on which RAT is selected. Past experience has shown that lower energy consumption, which translates directly into longer battery life between charges, is a key criterion in ensuring consumer satisfaction with mobile devices.